Sound reproducing and receiving device



April II, 1944.

F. HARRISON l y J ,IM

l 5 Sheets-Sheet 1 /N new Tae mit I "i April 11, 1944.

Filed-Feb. 11, 1942 3 Sheets-Sheet 2 O wus/vree 50m# #42e/Sao April u, 1944. F. HARRISON, 2,346,429

SOUND REPRODUCING AND RECEIVING DEVICE Filed Feb. 11, 1942 5 Sheets-Sheet 3 /fwE/v me Ffm/M HiFi/50N romance.

soUNn anrnonucmd AND RECEIVING DEVICE Frank Harrison, Braintree, England Application February 11, 1942, Serial No. 43II,450 In Great Britain December Z0, 1940 2 claims.

The invention relates to sound reproducing or receiving devices of the type wherein an iron amature, connected to and actuating an acoustic diaphragm is acted on by magnetism which is varied in strength and rapidity by an electric current passing through a coil or coils. The magnetism is generally supplied by a permanent magnet.

One object of the present invention is to provide a sound repoducer or receiver which is of .l

less expensive construction than the average type of moving coil instruments and eifectsI a. considerable economy in the weight of metal required for the magnet, whilst having a satisfactory per- Another object of the invention is to provide a device which operates in a satisfactory manner under water.

According to the present invention a sound reproducing or receiving device wherein a cone diaphragm is mounted in a chassis, is characterised in that spaced openings are provided between the rimof the diaphragm and a peripheral flange on the chassis to which the diaphragm is connected so as to allow fluid, such as water, in which the device is located to pass to both sides of the diaphragm, whereby the pressure o! the uid acts uniformly on both sides of the diaphragm.

The invention will now be described by way ot example with reference to the accompanying drawings, wherein:

Figure 1 is a sectional elevation of one form of a device according to the invention.

Figure 2 shows a detail of a modified form of 35 construction.

Figure 3 is a partial sectional elevation of another form of construction.

Figure 4 shows a partial sectional elevation of a magnet system and an armature.

Figures 5 and 6 show a side elevation and end view of a bridge.

Figure '7 shows a sectional elevation of a form of device for operation in water, and

Figure 8 shows a detail view of a portion of the device shown in Figure 7.

Referring nrst to Figure l, I is an amature in the form of a thin iron plate of large area provided with a rim 2 at right angles thereto and by which it is secured to a chassis 3 provided with a central aperture 4. The disc I is connected, from a point at or near its center, by a thin springy wire or stem 5 to the apex of a conical acoustic diaphragm 6, orrloud speaker The chassis 3 is provided with openings l so as to allow the surrounding uid to pass to the back of the cone 6. The cone 8 is secured at its periphery to a peripheral ange 8 of the chassis 3 by a suitable adhesive, preferably with the assistance of a layer of felt 9 or other absorbent material. The periphery of the cone 6 is preferably crimped in the usual manner.

The wire or stem 5 connecting the armature I to the cone 6 may be of brass or iron, preferably a length of piano wire which is sufliciently resilient to allow for a slight change of angle between the armature I and the cone 6 when in operation. A shortstem which does not bend is suitable for bass notes and sensitivity, but substantially dampens higher frequencies, whilst a stem which is too thin and springy weakens the bass and sensitivity.

In order that the wire may produce satisfactory results in all cases, it is first bent at right angles with a small radius of curvature as at Ill, not a sharp bend, the right angled Vportion II being soldered to the armature I. The stem is preferabLv provided with a further bend as at I2 so that the stem is no longer straight. This bend is very shallow. By soldering the part II to one side of the armature, the other side thereof is left smooth. It will. however, be understood that the wire 5 may be secured tothe amature I in $0 other ways. The wire 5 may be screwed and secured to the armature by nuts located on opposite sides ofthe armature I. In such a case the bend I2 may be more pronounced, the nuts being so positioned that when a horse shoe magnet I3 isused, they come between the pole pieces of the latter. In this case the nuts and wire are preferably of brass or other non-magnetic material.

One method of connecting the wire 5 to the cone B consists in securing a small conical washer I4 of brass foil to the outside of the cone 6, at the apex thereof, by adhesives. Over this washer I4 and to the adjacent surface of the cone 6 there is secured by adhesive a ring or band I5 of thin paper. The periphery of the brass washer I4 is thus sandwiched between the cone 6 and the band or ring I5. 'I'he wire 5 passes through holes in the apex oi the cenet and the washer Il and is soldered to the latter from inside the -cone 6 through the hole in the apex thereof.

-The wire 5 may however be secured to the cone i in other ways. For example the end of the wire I may be screw-threaded and secured in P0- sition by complementary conical washers on the inside and outside of the apex of the cone 8 and nuts.

The cone 3 may be made of any suitable material such as drawing paper, thin blotting paper, moulded paper, fabric or thin metal. The material may be treated in any suitable manner to render it weather and water-proof.

The cone may be shallow or deep. The armature I may also be connected directly at its periphery to the cone 6. The annular rim `2 of the armature may be at right angles or at any suitable angle to the flat portion. The connection may, for example, be eifected by suitable binding material coated with adhesive. -On the chassis' 3 there is mounted, by means of a bolt I 8, a bridge I1 of any suitable material preferably of a synthetic nature. spring I9 is mounted between a nut I3 and washer 20 and the chassis 3. Between the bridge I1 and the chassis 3 is provided packing against which the bridge I1 bears with line contact at 22 by providing the bridge I1 with a pointed edge at this point. In the bridge I1 is mounted a permanent horse-shoe magnet I3 which is secured in position by a cover plate 23. Coils, 24 adapted to be connected to a suitable amplifier, are arranged around the limbs of the magnet I3 which are generally of rectangular cross section.

In order to adjust the air gap between the magnet poles and the armature I, an adjusting screw 25 passes through the bridge I1 and engages with point contact with the chassis 3. The screw 25 is provided with a ribbed operating knob 26 with which there co-operates a spring 21, secured to the bridge I1, to prevent accidental turning of the screw 25. The knob 28 may be used for volume control.

As will be readily understood, the armature I may be extended to form the chassis 3, whereby these parts are formed as a single member. By slightly displacing the center at which the magnetic force acts on the armature I, for example, by locating the magnet I3 as shown in Figure 2, predetermined parts of the frequency response curve can be favored.

Similar results are obtained by displacing the point of attachment of the wire to the armature I or both by displacing the magnet I3 and the point of attachment of the wire 5.

However, the central arrangement of the magnet I3 and point of attachment of the wire 5 gives best bass reproduction, the "ofi center position favors treble notes and sensitivity.

The size or diameter of the armature I relatively to its thickness is important. A predetermined thickness is necessary in order to utilize fully the magnetism employed. T00 small a diameter of the armature l renders the latter too stiff or rigid, thus reducing sensitivity.

The diameter of the armature I may be large and the bridge I1 may be bolted thereto within its periphery or at the edge of its periphery.

The chassis may be of the same shape as an On the bolt I9 a ordinary loud-speaker chassis but made of thin loud-speaker chassis may have a projecting rim stamped therefrom around a central opening therein, this rim being provided with a continuous or interrupted screw thread. A rimmed metal plate, similar to that usually employed for closuring jars and having a screw thread corresponding with the screw thread on the chassis rim, may be screwed on to the latter so as to form an armature connected to the cone, in the manner above described. A disc armature may be used which is clamped on the chassis boss by an internally screwed ring engaging with a corresponding external thread on the boss and having an internal flange bearing against the armature.

In the construction shown in Figure 3 a chassis 21a constructed of suitable material, preferably of the material sold under the registered trademark Bakelite is provided with a suitable number of arms 23 of suitable section such as circular, oval or channel, and with a central internally screwed boss 29. Adisc armature 30 is fitted into the boss 29 and is pressed against a seating 32 byaringnut 3|.

The wire 5 is connected to the armature 30 and cone 8 in the manner above described. A body 33 supporting the magnet I3 and coils 24 is screwed into the boss 29 for adjusting the magnetic gap between the magnet I3 and the armature 30. The magnet I3, as shown, extends from the body 33 to allow for the nut 3| plus suicient clearance for adjusting purposes. The body 33 is provided with passages 34 for the wires leading to the coils 24. The body 33 is provided with a Vmilled or grooved portion 35 for engagement by a spring 36, secured to the boss 29, so as to prevent accidental turning of the body 33.

One or more additional springs 31, secured to the arms 28, press against the back of the body 33 to hold it against the screw thread in the boss 29. The rotation of the body 33 may serve for volume control by increasing or reducisrg the gap between the magnet I3 and armature This arrangement for a dust proof air gap facilitates renewal of the armature. It also provides for a satisfactory bass and sensitivity.

In Figure 4 is shown a bridge 39 which may be formed by stamping, casting or moulding, any suitable material, for example a strip of iron, provided with two feet or lugs 39, 40. The lugs 39, 40 and the bridge 38 are preferably curved transversely for the purpose of strength.

The foot 39 is longer than the foot 40 and bears against the armature or the chassis 4I, with line contact at 42. The foot 39 is bolted to the armature I or to the chassis 4I by a bolt I6 in the manner described above in connection with Figure 1.

Through the shorter foot 40 passes the adjusting screw 25. This adjusting screw 25 may bear against the armature as shown in Figure 4 or against the chassis as shown in Figure l.

When the adjusting screw 25 bears against the armature, the high notes may be influenced by carefully selecting the point at which the screw-25 contacts with the armature between the centre and the periphery thereof. Direct contact between the screw 25 and the armature is preferable and is also most satisfactory for sensitivity. With this arrangement. the bridge 33 and the parts carried thereby may be made small and light in weight and arranged centrally and diametrically across a large armature I. When the bridge 38 is secured to the chassis 3 as shown in Figure 1, it is larger and more robust and spans the armature I.

When soft iron pole pieces 43 are used which are excited by a magnet 44 and coils 24, the

bridge 38 is of brass or other non-magnetic material of channel section, as shown at 45 in Figures and 6. The pole pieces 43` are simple right angle bends and the limb parts for coils are passed through a rectangular hole 46 in the bridge 45 when made of brass or through two slits in the latter when the bridge is not of metal. The yoke parts 41 of the pole pieces 43 rest on the bridge 45 and are oppositely directed. The magnet 44' is a short bar magnet of high intensity iiux such as cobalt steel, and is placed across the yoke parts 41 and bolted to the'bridge as indicated at 48. In order to avoid the necessity of drilling or slotting the magnet 44, this may be replaced by two narrow magnet bars of which like poles are placed adjacent to one another, these bars being located on opposite sides of the bolts, washers bridging the two bars adjacent their ends.

Laminated pole pieces may be used in which case projections are provided at the ends-of the yoke so as to short circuit the magnetism from the armature thus forming an alternative path for the ux when the device is in operation. In this case the bar magnet or magnets are Slightly bent at the middle so as to clear the projections magnetically.

It has been found that the extreme bass notes depend to a large extent on the rigidity of the material which supports the armature and magnet and which is located between these parts. In addition to solidity of construction, such as embedding the body cf the magnet in a hard moulded material, Poissons ratio for the material is of importance. Porcelain used in electrical work, or similar hard brittle material, is very suitable for the purpose.

By the use of synthetic plastic materials for the bridge: a considerable economy in metal is effected.

The simplest form of a combined armature and chassis is a broad strip of iron bent in the form of a sectional view of a loud-speaker chassis. The magnet assembly is bolted to the vertical part which constitutes the back plate. The edges may be bent round or coiled for obtaining stiiness.

With a large armature, corresponding substantially with the lid of a wax-polish tin, two or more arms may be secured to its rim, the free ends of the arms being adapted to be secured to a baille board. A combined armature and chassis of this character may however be stamped as a single unit in which case the rim is outwardly inclined at an angle instead of being at right angles.

An advantage of using a sheet or disc armature l rmly supported at its periphery or at a substantial part thereof is that the amplitude of the central portion is limited by a resistance which increases considerably as the center of the armature approaches the pole faces, this resistance tending to equal the greatly increasing strength of attraction due to the square of distance law between pole and armature. This action coupled with the load applied to armature by the cone diaphragm, enables a very fine air gap to be used, whereby good sensitivity is obtained. The amplitude required for producing loud low organ notes appears to be extremely small. (This applies to actual music which is complete with harmonics and does not necessarily hold for a low frequency pure sine wave test.) By reason of this ne gap the adjusting screw 25 is provided with a large knob 26 to control theiine adjustment. In Figure 4 a separate milled portion 26a is provided on the screw 25 for engagement by the spring 21.

Another advantage of a sheet or disc armature is that its large surface area assists in catching the stray field and in concentrating this eld at the pole faces. The area of the faces of the pole pieces may be less than their own cross sectional area to enhance this concentration.

The two controlling coils may be arranged in series or in parallel, the' series arrangement is most suitable for microphone work and the parallel system for loud speaker work. The magnet may be of the soft iron energized type. The pole pieces may be wound of low resistance for use with an output transformer.

Instead of two coils and a double pole magnet, a single pole and one coil may be used, in which latter case the other pole is located at the periphery of the armature or over the chassis, Packing is provided on the leg orclip by which the second pole is bolted to the armature or chassis. In the case of a single pole arrangement half the armature is included in the magnetic iield, whilst the bridge is replaced by the magnet. The lug or foot provided with the adjusting screw is bolted to the central pole together with the soft iron pole piece, the lug and adjusting screw being of brass or other non-magnetic metal.

With a single pole the most satisfactory reproduction is obtained, but as the magnetic circuit is longer than in the case of two poles the system is less sensitive. The shorter the circuit, including the magnet, the greater the sensitivity.

The cone diaphragm or the chassis to which it is fastened, may be secured to a baille board which may be a frame of which the sides are arranged at right angles or at another suitable angle to one another and resembling the front of a `loud speaker cabinet.

The depth of the sides is such as to form a tray instead of a box or cabinet. Even a flat frame produces a baiile eiTect which is increased by the addition of shallow sides. The entire absence of box or cabinet resonance, coupled with good bass response, yields a type of reproduction suitable for many purposes. The tray baille may be supported at the back by a wire loop and set on a tableat an angle.

The chassis or rim ofthe cone diaphragm is screwed or otherwise fastened to the back or inside the tray. The tray baflie may be constructed of wood, china, porcelain, earthenware, moldable material or metal. A

The chassis or diaphragm may be secured toa circular frame supported horizontally by three legs, the unit being at the bottom. A loading horn'may'be fitted on the frame. The horn may be of a slightly tapered tube shape, the smallest diameter being substantially equal to the diameter of the diaphragm. The major diameter end of'the tube may be cut oi at an angle. The horn or tube may be of any suitable length, the bass response being increased even' by one of short length. The tube may be made of thin cardboard or other suitable material.

The device may be mounted in a cabinet or loaded by an exponential horn.

Referring now to Figures 7 and 8, showing an arrangement for emitting or receiving music, speech or other sound under water, the various parts are of similar construction to those described with reference to the other iigures.

. The cone 6 is. preferably of thin material and of light construction and is secured to the chassis 3 by a series of preferably equally spaced strips or lugs 50 of corrugated metal. In this case the chassis is preferably of circular shape and is mounted in a substantially semi-spherical casing 5I adapted to be fitted into a circular hole in the side 52vof a vessel, for example, a submarine. The chassis 3 is also apertured as indicated at 53 so that water can pass to both sides of the cone 6 and also to the back of the armature l, and in fact also around the magnet assembly. The magnet i3 and coils are completely enclosed, but with a small air space around the coils, in a molded mass forming the bridge 55, only a small part of the pole pieces being exposed to water. In this case the gap between the armature I and the poles of the magnet I3 is a water gap. One end of the coils is bare to the water.

All the metal parts in contact with water arev suitably protected, for example, by electro-plating. The adjusting screw 25 is connected by a universal joint 56 to a stem 51 passing through a gland 58 and operated'from inside the vessel by a knob 59.

The bridge 55 is bolted to the chassis 3 through the medium of an insulating bush 60 of fairly hard material and is insulated electrically from the armature i.

Theuniversal joint 56 is provided with insulating bushes so as to separate the gland 58 from electrical connection with the chassis 3 or armature I.

Insulated wires `are passed through a gland 6l, one wire leading to the armature l and another to the pole pieces and these lead to the inside of the vessel. This arrangement includes a small battery of say 2 volts and a meter or signal lamp to indicate whether or not the armature is free of the pole pieces. The resistance of the sea water is sufficient to show a diiierence against direct contact. The main input cable is connected to an amplifier inside the vessel. The cone 6 is protected by a strong grid or bars 62 extending over the cone 6 and covered by a strong fine wire mesh gauze 63 secured to the grid. The grid is preferably level with the contour of the side of the vessel.

A small bag or skin containing air may be placed at the back inside the recess receiving the device.

The cone 6 of light construction may be of any suitable size, satisfactory results being obtained with a cone about-14 inches in diameter.

The recess for receiving the device is made of suiiicient size to give four or five inches of clearance of water around the cone and armature. It will, however, be understood that this clearance may be increased.

A vessel equipped according to the invention for example, a submarine, even when submerged ,can communicate with other vessels, including surface, coast stations or harbors equipped in a similar manner.

As the coils for a receiver have a large number of turns and are arranged in series and for a transmitter a smaller number of turns and are arranged in parallel, preferably both types are provided one for reception and the other for transmission. More than one of each type may be used and placed at different parts around the hull of the vessel below the water line.

A device as above described may be submerged at a suitable point, for example, a harbor, at the end of a long cable, the gap preferably being fixed, the device being completely surrounded by water and protected by a frame covered with wire gauze.

The bridge 38 may be formed and the yokes of the pole pieces 43 and magnet. may be em-V bedded in moldable material.

As shown in Figure 7 the magnet I3 and coils 24 may be mounted in an opening of the bridge 55. The opening is closed by cement 62a covered by a plate 63a bolted to the bridge as indicated at 64.

Where it is desired to extend the length of the adjusting screw 25 the knob 26 is provided with a projection of irregular shape for the reception of an extension member, preferably of rubber, which is provided with a cup which ilts over the knob 26 and with a recess to receive the projection and of the same shape as this.

The screw 25 may engage with a split nut member secured to the bridge, the screw engaging with a recess in the chassis. In an alternative arrangement a cup, for engagement by the screw 25, may be secured to the chassis.

What I claim is:

1. In a device of the character described, the combination comprising a. chassis, a cone diaphragm, a resilient mounting for the periphery of said cone, a sheet iron armature associated with sad chassis, a resilient stem secured to one face of said armature and to the apex of said cone, a magnet system operatively associated with said armature, a bridge in which said magnet system is mounted, said bridge being arranged to rock about one end, and having a hole therein at said end, a pin passing through said hole and an aligned hole in the chassis, a spring carried upon said pin, said spring serving to yieldably draw said bridge against said chassis so that the bridge seats against the chassis, and adjusting means associated with the other end of said bridge for adjusting said magnet system relatively to said armature against the drawing action of said spring.

2. A device according to claim 1 in which said pin is adjacent the outer edge of said armature.

FRANK HARRISON. 

